1. Field of the Invention
Cutting head assemblies, particularly those used for cutting steel structural members and the like. Such circular cutting drills are usually employed together with a centering or pilot drill which cuts a centering hole, prior to engagement of an outer circular drill with the surface to be cut.
2. DESCRIPTION OF THE PRIOR ART
Prior art investigation has developed the following: WEBSTER 58,924, HEYDENREICH 475,559, BERNAY 1,359,955, McGRATH 1,940,220, GONZALEZ 2,496,939, TREVATHAN 3,390,596.
Webster teaches a metal circular drill having a bore therein. Positioned within the drill and urged outwardly is a pointed member "d" which is centrally located. Member "d" is positioned on a punch mark to hold the drill in the desired spot. As the drill advances into the work the inner member "d" recedes into the outer drill body.
Heydenreich shows a plug cutter consisting of an outer circular cutter A with cutter teeth E and having a bore longitudinally therethrough. Within the bore is positioned another cutter N having a stem H projecting therefrom and adapted to slide within the outer cutter. A spring urges the inner cutter N downwardly. The outer and inner cutter rotate simultaneously.
Bernay discloses a drilling device including a shank portion 1, body portion 7 and drill 16, 17. The body portion has a bore therethrough and at the lower end is positioned an apertured plug 9 with spring 11 urging the plug downward. The cutting tool 16, 17 is positioned within a slot in 12, in the body portion, and held in place by plug 9. Lubricant in passageway 2, the bore in the body, hole in plug 9 and over the cutting tool. The device does not include an inner and outer tool.
McGrath discloses a boring tool having an outer pipe-like member 11 with cutters 31 at one end. Positioned within member 11 is a smaller concentric pipe also having cutters at one end. The inner and outer cutters are designed to operate simultaneously with one cutter making a small hole and the outer cutter enlarging the hole. The small cutter is lubricated via the passageway in the inner pipe, and the large cutter by fluid in the outer pipe.
Gonzalez shows in FIG. 3 a circular drill member 70 having a centering plug 75 positioned therein. A spring 76 urges the plug downward to locate the drill on a mark such as a punch mark. As the drill proceeds to cut, the plug 75 moves upwardly.
Trevathan teaches a cutting head assembly having a circular cutter 25 with a bore therein. Positioned within the bore is a pilot drill 55. The circular cutter and pilot drill rotate simultaneously. Slidably positioned on the pilot drill is a disc 55 urged downwardly by spring 69. When drilling into material, and after the cut is completed, the disc discharges the circular piece of material in the circular cutter.